Anal Bioanal Chem DOI 10.1007/s00216-013-7606-6
TRENDS
Medical applications of breath hydrogen measurements Woosuck Shin
Received: 5 September 2013 / Revised: 12 December 2013 / Accepted: 29 December 2013 # Springer-Verlag Berlin Heidelberg 2014
Abstract In this article, technical developments in breath analysis and its applications in the field of clinical diagnosis and the monitoring of various symptoms, particularly molecular hydrogen in breath, are introduced. First, a brief overview of the current uses of the hydrogen breath test is provided. The principles of the test and how hydrogen can be used as a biomarker for various symptoms, and monitoring microbial metabolism, are introduced. Ten case-study applications of breath hydrogen measurements for which hydrogen exhibits beneficial effects for diagnosis, including the contexts of oxidative stress, gastrointestinal disease, and metabolic disorders, are discussed. The technologies and problems involved in breath hydrogen testing, sampling, pretreatment, and detection in exhaled breath are discussed, and research including current analytical systems and new sensors is focused on in the context of hydrogen detection. Keywords Breath analysis . Gastrointestinal disease . Hydrogen . Methane . Gas sensor . Orocecal transit time
Introduction Medical gases are expected to provide us with more effective therapeutic interventions and preventive medicine in the future. In recent decades, there has been an extraordinarily rapid growth in our knowledge of gaseous molecules, including nitric oxide, carbon monoxide, hydrogen, and hydrogen sulfide, which are known to play important roles in biological systems. Among them, the flammable gases hydrogen and methane at levels of approximately several parts per million Published in the topical collection Chemosensors and Chemoreception with guest editors Jong-Heun Lee and Hyung-Gi Byun. W. Shin (*) Electroceramics Processing Group, Advanced Manufacturing R.I., AIST, Shimo-Shidami, Moriyama-ku, Nagoya 463-8560, Japan e-mail: [email protected]
are produced by intestinal bacteria, and their concentrations in human breath have been used to monitor microbial metabolism in the colon (Fig. 1) [1, 2]. Breath hydrogen reflects carbohydrate fermentation in the colon as shown in Fig. 1. When unabsorbed carbohydrate enters the colon, it is rapidly fermented by anaerobic colonic bacteria, producing short-chain fatty acids that liberate not only carbon dioxide but also the flammable gases hydrogen and methane [3]. Analysis of breath hydrogen provides a measure of orocecal transit time (OCTT) [4] (also known as small bowel transit time), colonic fermentation, abnormal fermentation, galactose and/or lactose intolerance [5], and sometimes irritable bowel syndrome [6]. A recent study in animal models of cerebral infarction revealed that hydrogen gas plays an important role in inactivating sources of oxidative stress such as hydroxyl radicals. A recent article [7] on the effects of molecular hydrogen on reactive oxygen species showed the potency of hydrogen as a therapeutic gas for oxidative-stressmediated diseases, including cerebral infarction. Both basic and clinical hydrogen research have recently resurfaced in Japan. Following the aforementioned report [7], related meetings of medical hydrogen research groups were organized, affording investigators opportunities to share the rapid progress in this new field, and commercial hydrogen-enriched water also appeared on the market as a kind of health care supplement. Owing to the potential advantages of the hydrogen breath test over other conventional medical tests, including its noninvasive nature and safety, breath hydrogen has attracted great attention in recent years. However, evaluation of the data from different approaches remains inconclusive owing to a lack of clinical validation of hydrogen breath tests, a lack of standardized procedures, and poor methods of validation. Further research is therefore required to expand the applicability of breath hydrogen testing in the clinical diagnosis of diseases. Some previous reports are introduced and discussed in the following sections.
W. Shin
Fig. 1 Hydrogen in breath is generated by intestinal bacteria. This fact is used in medical examinations to evaluate colonic flora
Why measure breath hydrogen and methane? Three major points are focused on in this review. One is the purpose of the measurement of breath hydrogen. Various applications of the measurement of breath hydrogen are summarized in Fig. 2. The most well known application of breath hydrogen measurement is to quantify OCTT. The second point of interest is how the breath sampling is performed and how subjects are prepared prior to it. Breath is collected in gasbags or condensed using solid-phase microextraction (SPME) [3]; the gasbag sampling method is now more popular than the breath condensate method. Numerous other factors are potentially important with regard to the subjects in breath hydrogen studies, including age, whether they were healthy or patients, symptoms, time of day of sampling, collection bag type, and whether they washed their mouth prior to sampling. The third point of interest is the measurement system used for breath analysis. Ideally, portable devices that selectively detect hydrogen rapidly should be used. Although gas chromatography (GC) has been used, mainly for the analysis of volatile constituents in breath samples, other techniques (e.g.,
Fig. 2 Some applications of the measurement of hydrogen in breath, and some potentially associated factors
sensors) have also been used satisfactorily. To improve their performance, there is a need to increase their tolerance to factors such as water vapor interference, which often leaves the sensor system desensitized to the gaseous biomarkers, and to enhance their selectivity. The importance of the methane breath test cannot be disregarded [8]. Even today, when hydrogen and methane are measured, there is a certain rate of false negatives for carbohydrate malabsorption. This can be due to colonic fermentation, gastrointestinal motor disorder, and the oral bacterial flora [6]. Because of this problem, measuring not only hydrogen but also methane or other gases should be advantageous [9]. In clinical practice, defining normal values of OCTT without knowledge of breath-methane-producing status may lead to misinterpretation of the result of the hydrogen breath test. Table 1 summarizes the clinical reports on the hydrogen breath test to date, with the purposes of the tests being described in Fig. 2, comparing the pretreatment methods, data acquisition methods, and detectors.
How hydrogen breath tests are used; case studies In clinics, the hydrogen breath test is typically used in the diagnosis of three conditions. The first is where dietary sugars are not digested normally. Lactose is the most commonly poorly digested sugar, and a person who is unable to digest lactose is known as lactose-intolerant. The second is for diagnosing bacterial overgrowth of the small bowel, by checking for abnormally large numbers of colonic bacteria in the small bowel or colon. The third is for diagnosing rapid passage of food through the small bowel. All three of these may cause numerous symptoms, such as abdominal pain, abdominal bloating and distention, flatulence (passing gas in large amounts), and diarrhea. The interpretation and use of the results of hydrogen breath tests depend on the subjects’ various symptoms and their diet, including factors such as sugar (lactose, sucrose, sorbitol), rice, milk, and hydrogen-enriched water. Individual differences in the patterns of hydrogen production following the ingestion of sugar are also an important aspect of the relationships among the digestion or absorption of sugar, the health of the subject, and breath hydrogen. Figure 3 shows typical breath hydrogen concentration over a time course in a patient with carbohydrate malabsorption. Usually, prior to testing, the subject fasts overnight and breath hydrogen is measured the next morning, after ingestion of a small amount of a test sugar (usually lactose). Breath samples are collected and analyzed every 15 or 30 min for 3–5 h. As well as the three contexts mentioned above, many researchers have investigated the use of breath hydrogen testing in other contexts. In this review, ten cases of diseases and
13 female students with no history of gastrointestinal disease. Sleeping and meals were controlled for 3 days 25 gastric ulcer patients
218 patients with lactose intolerance (male-tofemale ratio of 1:4) 15 disabled elderly people
30 patients
5 normal people, fasting for 15 h before the test
OCTT
OCTT
OCTT
Bone density
Small bowel bacterial overgrowth
Hydrogen-enriched water
Hydrogen-enriched water
Gastric emptying and OCTT in pregnancy
Circadian rhythm of breath hydrogen
Efficacy of lactulose plus 13C-acetate breath test
Lactose intolerance and bone mineral density and vertebral fractures Small bowel bacterial overgrowth and rice
Effect of hydrogen-enriched water on patients
Breath hydrogen produced by ingestion of commercial hydrogen-enriched water and milk
After an overnight fast (11 h), ingestion of 50 g of glucose or 200 g (cooked weight) of rice with 150 mL of green tea. Every 15 min for 6 h Effect of hydrogen-enriched water on patients with type 2 diabetes or impaired glucose tolerance; glucose and insulin were monitored End-alveolar breath was obtained every 5 min in a breath sampling bag
Breath was collected after the ingestion of 100 mg of 13C-acetate and 20 mL (12 g) of lactulose subsequently every 10 min for 2 h and additionally every 30 min for 4 h 1 day of fasting before ingestion of 50 g of lactose, every 30 min for 4 h
Breath was collected before the ingestion of 18 g of lactulose isoosmotic water solution (180 mL), and subsequently every 10 min for 4–6 h Breath was collected before and after the students went to bed, every 30 min
After ingestion of 25 g of lactose, 30-min interval, for 3 h Measured every 15 min for 6 h
Data acquisition
GC gas chromatography, MS mass spectrometry, OCTT orocecal transit time, SD standard deviation
The women fasted for more than 12 h before eating the test meal. 15 yong women and 13 elderly women 11 pregnant women
Age, sex, milk drinking habits OCTT
Breath hydrogen measurement OCTT in women
Pretreatment
Purpose
Topics
Table 1 Clinical reports on the hydrogen breath test
Gas chromatograph (model 12i, QuinTron Instrument)
Not for hydrogen
Mean ± SD
TRIlyzer mBA-3000 (Taiyo)
[24]
Unknown
Mean ± SD. Spearman’s correlation coefficient
Mean ± SD
[18]
TGA-2000 (Teramecs)
Below the baseline of 10 ppm hydrogen is discarded
[25]
[17]
[16]
[15]
MiroLyzer (Quintron instruments)
Mean ± SD
[14]
[13]
[12]
Reference
MicroLyzer model 12 gas chromatograph (QuinTron Instrument)
MicroLyzer and GC–MS compared MicroLyzer (QuinTron Instrument)
Detector
Mean ± SD
Mean ± SD
Mean ± SD
Data analysis
Medical applications of breath hydrogen measurements
W. Shin
With regard to an optimal analyzer system or test method, gas sensing systems should be insensitive to confounding factors such as age, gender, smoking habits, and lifestyle. However, other difficulties associated with these confounding factors render the standardization of breath hydrogen testing difficult to implement in the clinic. Despite these limitations, the fundamental conclusions of this early study are important, and further similar basic studies should be undertaken to clarify the results. A meal-based study investigating differences in age Fig. 3 Change of hydrogen gas concentration in the hydrogen breath test indicating carbohydrate malabsorption. Orocecal transit time (OCTT), which is also known as small bowel transit time (SBTT), is evaluated by the hydrogen breath test
physiological states for which hydrogen exhibits any sign of symptoms or beneficial effects are discussed in the following sections. Unfortunately, the base level of breath hydrogen in Fig. 3 is still unclear. There is no clear report on the average level of hydrogen and methane in the breaths of normal people, and the gas levels change easily with the food intake. Several reports have shown that fasting basal hydrogen and methane concentrations in normal people’s breath in the morning are extremely low—several parts per million to 8 ppm [9] or 10 ppm [10] for hydrogen and 1 ppm to several parts per million for methane. However, the linearly calibrated detection ranges of some instruments used were in the range from 2 to 200 ppm and the reliability in the several parts per million range was relatively low, so hydrogen concentration at the parts per million level is rarely considered in clinical reports. In some patients, colonic obstruction can be the origin of the increase in hydrogen and methane levels in breath. Urita et al. [11] reported a remarkably high fasting breath methane level in a patient with volvulus of the sigmoid colon, suggesting both hydrogen analysis and methane analysis can be a tool for evaluating the intestinal circumstances. Gender, age, symptoms, and milk drinking habits An early report [12] investigated fundamental questions related to breath hydrogen measurement, particularly how gender, age, and symptoms such as lactose intolerance can affect the hydrogen concentration in breath. The authors of that report also tested the validity of various measurement methods. They assessed both typical GC and a commercial gas breath analyzer (MicroLyzer, QuinTron Instrument), and concluded that the MicroLyzer-based method is much easier to use, and more precise. In their study, breath hydrogen concentrations were not significantly associated with gender, age, or any specific symptoms, and there was no association between breath hydrogen and milk drinking habits.
In a meal-based study investigating differences in age, Kagaya et al. [13] used breath hydrogen concentration not only as a measure of OCTT but also to investigate the levels of carbohydrate fermentation in the colon. They concluded that carbohydrate fermentation in the colon was much higher in younger women than in elderly women. They reported that there was a secondary peak in the young group that was much higher than that in the elderly group. It was surmised that this was due not only to differences in baseline hydrogen levels, but also to hydrogen that had been recently produced by colonic bacteria after ingestion of dietary fiber in a test meal. OCTT in 15 young women and 13 elderly women was assessed by measuring breath hydrogen concentrations after they had consumed a solid test meal. The difference between the two groups was significant (p
TRENDS
Medical applications of breath hydrogen measurements Woosuck Shin
Received: 5 September 2013 / Revised: 12 December 2013 / Accepted: 29 December 2013 # Springer-Verlag Berlin Heidelberg 2014
Abstract In this article, technical developments in breath analysis and its applications in the field of clinical diagnosis and the monitoring of various symptoms, particularly molecular hydrogen in breath, are introduced. First, a brief overview of the current uses of the hydrogen breath test is provided. The principles of the test and how hydrogen can be used as a biomarker for various symptoms, and monitoring microbial metabolism, are introduced. Ten case-study applications of breath hydrogen measurements for which hydrogen exhibits beneficial effects for diagnosis, including the contexts of oxidative stress, gastrointestinal disease, and metabolic disorders, are discussed. The technologies and problems involved in breath hydrogen testing, sampling, pretreatment, and detection in exhaled breath are discussed, and research including current analytical systems and new sensors is focused on in the context of hydrogen detection. Keywords Breath analysis . Gastrointestinal disease . Hydrogen . Methane . Gas sensor . Orocecal transit time
Introduction Medical gases are expected to provide us with more effective therapeutic interventions and preventive medicine in the future. In recent decades, there has been an extraordinarily rapid growth in our knowledge of gaseous molecules, including nitric oxide, carbon monoxide, hydrogen, and hydrogen sulfide, which are known to play important roles in biological systems. Among them, the flammable gases hydrogen and methane at levels of approximately several parts per million Published in the topical collection Chemosensors and Chemoreception with guest editors Jong-Heun Lee and Hyung-Gi Byun. W. Shin (*) Electroceramics Processing Group, Advanced Manufacturing R.I., AIST, Shimo-Shidami, Moriyama-ku, Nagoya 463-8560, Japan e-mail: [email protected]
are produced by intestinal bacteria, and their concentrations in human breath have been used to monitor microbial metabolism in the colon (Fig. 1) [1, 2]. Breath hydrogen reflects carbohydrate fermentation in the colon as shown in Fig. 1. When unabsorbed carbohydrate enters the colon, it is rapidly fermented by anaerobic colonic bacteria, producing short-chain fatty acids that liberate not only carbon dioxide but also the flammable gases hydrogen and methane [3]. Analysis of breath hydrogen provides a measure of orocecal transit time (OCTT) [4] (also known as small bowel transit time), colonic fermentation, abnormal fermentation, galactose and/or lactose intolerance [5], and sometimes irritable bowel syndrome [6]. A recent study in animal models of cerebral infarction revealed that hydrogen gas plays an important role in inactivating sources of oxidative stress such as hydroxyl radicals. A recent article [7] on the effects of molecular hydrogen on reactive oxygen species showed the potency of hydrogen as a therapeutic gas for oxidative-stressmediated diseases, including cerebral infarction. Both basic and clinical hydrogen research have recently resurfaced in Japan. Following the aforementioned report [7], related meetings of medical hydrogen research groups were organized, affording investigators opportunities to share the rapid progress in this new field, and commercial hydrogen-enriched water also appeared on the market as a kind of health care supplement. Owing to the potential advantages of the hydrogen breath test over other conventional medical tests, including its noninvasive nature and safety, breath hydrogen has attracted great attention in recent years. However, evaluation of the data from different approaches remains inconclusive owing to a lack of clinical validation of hydrogen breath tests, a lack of standardized procedures, and poor methods of validation. Further research is therefore required to expand the applicability of breath hydrogen testing in the clinical diagnosis of diseases. Some previous reports are introduced and discussed in the following sections.
W. Shin
Fig. 1 Hydrogen in breath is generated by intestinal bacteria. This fact is used in medical examinations to evaluate colonic flora
Why measure breath hydrogen and methane? Three major points are focused on in this review. One is the purpose of the measurement of breath hydrogen. Various applications of the measurement of breath hydrogen are summarized in Fig. 2. The most well known application of breath hydrogen measurement is to quantify OCTT. The second point of interest is how the breath sampling is performed and how subjects are prepared prior to it. Breath is collected in gasbags or condensed using solid-phase microextraction (SPME) [3]; the gasbag sampling method is now more popular than the breath condensate method. Numerous other factors are potentially important with regard to the subjects in breath hydrogen studies, including age, whether they were healthy or patients, symptoms, time of day of sampling, collection bag type, and whether they washed their mouth prior to sampling. The third point of interest is the measurement system used for breath analysis. Ideally, portable devices that selectively detect hydrogen rapidly should be used. Although gas chromatography (GC) has been used, mainly for the analysis of volatile constituents in breath samples, other techniques (e.g.,
Fig. 2 Some applications of the measurement of hydrogen in breath, and some potentially associated factors
sensors) have also been used satisfactorily. To improve their performance, there is a need to increase their tolerance to factors such as water vapor interference, which often leaves the sensor system desensitized to the gaseous biomarkers, and to enhance their selectivity. The importance of the methane breath test cannot be disregarded [8]. Even today, when hydrogen and methane are measured, there is a certain rate of false negatives for carbohydrate malabsorption. This can be due to colonic fermentation, gastrointestinal motor disorder, and the oral bacterial flora [6]. Because of this problem, measuring not only hydrogen but also methane or other gases should be advantageous [9]. In clinical practice, defining normal values of OCTT without knowledge of breath-methane-producing status may lead to misinterpretation of the result of the hydrogen breath test. Table 1 summarizes the clinical reports on the hydrogen breath test to date, with the purposes of the tests being described in Fig. 2, comparing the pretreatment methods, data acquisition methods, and detectors.
How hydrogen breath tests are used; case studies In clinics, the hydrogen breath test is typically used in the diagnosis of three conditions. The first is where dietary sugars are not digested normally. Lactose is the most commonly poorly digested sugar, and a person who is unable to digest lactose is known as lactose-intolerant. The second is for diagnosing bacterial overgrowth of the small bowel, by checking for abnormally large numbers of colonic bacteria in the small bowel or colon. The third is for diagnosing rapid passage of food through the small bowel. All three of these may cause numerous symptoms, such as abdominal pain, abdominal bloating and distention, flatulence (passing gas in large amounts), and diarrhea. The interpretation and use of the results of hydrogen breath tests depend on the subjects’ various symptoms and their diet, including factors such as sugar (lactose, sucrose, sorbitol), rice, milk, and hydrogen-enriched water. Individual differences in the patterns of hydrogen production following the ingestion of sugar are also an important aspect of the relationships among the digestion or absorption of sugar, the health of the subject, and breath hydrogen. Figure 3 shows typical breath hydrogen concentration over a time course in a patient with carbohydrate malabsorption. Usually, prior to testing, the subject fasts overnight and breath hydrogen is measured the next morning, after ingestion of a small amount of a test sugar (usually lactose). Breath samples are collected and analyzed every 15 or 30 min for 3–5 h. As well as the three contexts mentioned above, many researchers have investigated the use of breath hydrogen testing in other contexts. In this review, ten cases of diseases and
13 female students with no history of gastrointestinal disease. Sleeping and meals were controlled for 3 days 25 gastric ulcer patients
218 patients with lactose intolerance (male-tofemale ratio of 1:4) 15 disabled elderly people
30 patients
5 normal people, fasting for 15 h before the test
OCTT
OCTT
OCTT
Bone density
Small bowel bacterial overgrowth
Hydrogen-enriched water
Hydrogen-enriched water
Gastric emptying and OCTT in pregnancy
Circadian rhythm of breath hydrogen
Efficacy of lactulose plus 13C-acetate breath test
Lactose intolerance and bone mineral density and vertebral fractures Small bowel bacterial overgrowth and rice
Effect of hydrogen-enriched water on patients
Breath hydrogen produced by ingestion of commercial hydrogen-enriched water and milk
After an overnight fast (11 h), ingestion of 50 g of glucose or 200 g (cooked weight) of rice with 150 mL of green tea. Every 15 min for 6 h Effect of hydrogen-enriched water on patients with type 2 diabetes or impaired glucose tolerance; glucose and insulin were monitored End-alveolar breath was obtained every 5 min in a breath sampling bag
Breath was collected after the ingestion of 100 mg of 13C-acetate and 20 mL (12 g) of lactulose subsequently every 10 min for 2 h and additionally every 30 min for 4 h 1 day of fasting before ingestion of 50 g of lactose, every 30 min for 4 h
Breath was collected before the ingestion of 18 g of lactulose isoosmotic water solution (180 mL), and subsequently every 10 min for 4–6 h Breath was collected before and after the students went to bed, every 30 min
After ingestion of 25 g of lactose, 30-min interval, for 3 h Measured every 15 min for 6 h
Data acquisition
GC gas chromatography, MS mass spectrometry, OCTT orocecal transit time, SD standard deviation
The women fasted for more than 12 h before eating the test meal. 15 yong women and 13 elderly women 11 pregnant women
Age, sex, milk drinking habits OCTT
Breath hydrogen measurement OCTT in women
Pretreatment
Purpose
Topics
Table 1 Clinical reports on the hydrogen breath test
Gas chromatograph (model 12i, QuinTron Instrument)
Not for hydrogen
Mean ± SD
TRIlyzer mBA-3000 (Taiyo)
[24]
Unknown
Mean ± SD. Spearman’s correlation coefficient
Mean ± SD
[18]
TGA-2000 (Teramecs)
Below the baseline of 10 ppm hydrogen is discarded
[25]
[17]
[16]
[15]
MiroLyzer (Quintron instruments)
Mean ± SD
[14]
[13]
[12]
Reference
MicroLyzer model 12 gas chromatograph (QuinTron Instrument)
MicroLyzer and GC–MS compared MicroLyzer (QuinTron Instrument)
Detector
Mean ± SD
Mean ± SD
Mean ± SD
Data analysis
Medical applications of breath hydrogen measurements
W. Shin
With regard to an optimal analyzer system or test method, gas sensing systems should be insensitive to confounding factors such as age, gender, smoking habits, and lifestyle. However, other difficulties associated with these confounding factors render the standardization of breath hydrogen testing difficult to implement in the clinic. Despite these limitations, the fundamental conclusions of this early study are important, and further similar basic studies should be undertaken to clarify the results. A meal-based study investigating differences in age Fig. 3 Change of hydrogen gas concentration in the hydrogen breath test indicating carbohydrate malabsorption. Orocecal transit time (OCTT), which is also known as small bowel transit time (SBTT), is evaluated by the hydrogen breath test
physiological states for which hydrogen exhibits any sign of symptoms or beneficial effects are discussed in the following sections. Unfortunately, the base level of breath hydrogen in Fig. 3 is still unclear. There is no clear report on the average level of hydrogen and methane in the breaths of normal people, and the gas levels change easily with the food intake. Several reports have shown that fasting basal hydrogen and methane concentrations in normal people’s breath in the morning are extremely low—several parts per million to 8 ppm [9] or 10 ppm [10] for hydrogen and 1 ppm to several parts per million for methane. However, the linearly calibrated detection ranges of some instruments used were in the range from 2 to 200 ppm and the reliability in the several parts per million range was relatively low, so hydrogen concentration at the parts per million level is rarely considered in clinical reports. In some patients, colonic obstruction can be the origin of the increase in hydrogen and methane levels in breath. Urita et al. [11] reported a remarkably high fasting breath methane level in a patient with volvulus of the sigmoid colon, suggesting both hydrogen analysis and methane analysis can be a tool for evaluating the intestinal circumstances. Gender, age, symptoms, and milk drinking habits An early report [12] investigated fundamental questions related to breath hydrogen measurement, particularly how gender, age, and symptoms such as lactose intolerance can affect the hydrogen concentration in breath. The authors of that report also tested the validity of various measurement methods. They assessed both typical GC and a commercial gas breath analyzer (MicroLyzer, QuinTron Instrument), and concluded that the MicroLyzer-based method is much easier to use, and more precise. In their study, breath hydrogen concentrations were not significantly associated with gender, age, or any specific symptoms, and there was no association between breath hydrogen and milk drinking habits.
In a meal-based study investigating differences in age, Kagaya et al. [13] used breath hydrogen concentration not only as a measure of OCTT but also to investigate the levels of carbohydrate fermentation in the colon. They concluded that carbohydrate fermentation in the colon was much higher in younger women than in elderly women. They reported that there was a secondary peak in the young group that was much higher than that in the elderly group. It was surmised that this was due not only to differences in baseline hydrogen levels, but also to hydrogen that had been recently produced by colonic bacteria after ingestion of dietary fiber in a test meal. OCTT in 15 young women and 13 elderly women was assessed by measuring breath hydrogen concentrations after they had consumed a solid test meal. The difference between the two groups was significant (p
